Maxwell and Hertz Scientists and Electromagnetic Waves: Maxwell and Hertz About 150 years ago, James Clerk Maxwell, an English scientist, developed a scientific theory to explain electromagnetic waves. He noticed that electrical fields and magnetic fields can couple together to form electromagnetic waves. Neither an electrical field (like the static which forms when you rub your feet on a carpet), nor a magnetic field (like the one that holds a magnet onto your refrigerator) will go anywhere by themselves. But, Maxwell discovered that a CHANGING magnetic field will induce a CHANGING electric field and vice-versa. James Clerk Maxwell An electromagnetic wave exists when the changing magnetic field causes a changing electric field, which then causes another changing magnetic field, and so on forever. Unlike a STATIC field, a wave cannot exist unless it is moving. Once created, an electromagnetic wave will continue on forever unless it is absorbed by matter. Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and reception of radio waves. The unit of frequency of a radio wave -- one cycle per second -- is named the hertz, in honor of Heinrich Hertz. Hertz proved the existence of radio waves in the late 1880s.

He used two rods to serve as a receiver and a spark gap as the receiving antennae. Where the waves were picked up, a spark would jump. Hertz showed in his experiments that these signals possessed all of the properties of electromagnetic waves. Heinrich Hertz With this oscillator, Hertz solved two problems. First, timing Maxwell's waves. He had demonstrated, in the concrete, what Maxwell had only theorized - that the velocity of radio waves was equal to the velocity of light! (This proved that radio waves were a form of light!) Second, Hertz found out how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell's waves. Microwaves The existence of electromagnetic waves was predicted by James Clerk Maxwell in 1864 from his equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF region. The design necessarily used horse-and-buggy materials, including a horse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter whose parabolic cross-section worked as a reflection antenna. In 1894 J. C.

Bose publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves The microwave oven was invented as an accidental by-product of war-time (World War 2) radar research using magnetrons (vacuum tubes that produce microwave radiation, a type of electromagnetic radiation that has a wavelength between 1 mm and 30 cm). In 1946, the engineer Dr. Percy LeBaron Spencer, who worked for the Raytheon Corporation, was working on magnetrons. One day at work, he had a candy bar in his pocket, and found that it had melted. He realized that the microwaves he was working with had caused it to melt. After experimenting, he realized that microwaves would cook foods quickly - even faster than conventional ovens that cook with heat. The Raytheon Corporation produced the first commercial microwave oven in 1954; it was called the 1161 Radarange. It was large, expensive, and had a power of 1600 watts. The first domestic microwave oven was produced in 1967 by Amana (a division of Raytheon).

In 1967, Amana, a division of Raytheon, introduced its domestic Radarange microwave oven, marking the beginning of the use of microwave ovens in home kitchens. Although sales were slow during the first few years, partially due to the oven’s relatively expensive price tag, the concept of quick microwave cooking had arrived. In succeeding years, Litton and a number of other companies joined the countertop microwave oven market. By the end of 1971, the price of countertop units began to decrease and their capabilities were expanded. Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. Microwaves have wavelengths that can be measured in centimeters. The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven. Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke. Shorter microwaves are used in remote sensing.

These microwaves are used for radar like the doppler radar used in weather forecasts. Microwaves, used for radar, are just a few inches long. This microwave tower can transmit information like telephone calls and computer data from one city to another. How do we "see" using Microwaves? Radar is an acronym for "radio detection and ranging". Radar was developed to detect objects and determine their range (or position) by transmitting short bursts of microwaves. The strength and origin of "echoes" received from objects that were hit by the microwaves is then recorded. Because radar senses electromagnetic waves that are a reflection of an active transmission, radar is considered an active remote sensing system. Passive remote sensing refers to the sensing of electromagnetic waves which did not originate from the satellite or sensor itself. The sensor is just a passive observer. What do Microwaves show us? Because microwaves can penetrate haze, light rain and snow, clouds and smoke, these waves are good for viewing the Earth from space. The ERS-1 satellite sends out wavelengths about 5.7 cm long (C-band). This image shows sea ice breaking off the shores of Alaska.

The JERS satellite uses wavelengths about 20 cm in length (L-band). This is an image of the Amazon River in Brazil. This is a radar image acquired from the Space Shuttle. It also used a wavelength in the L-band of the microwave spectrum. Here we see a computer enhanced radar image of some mountains on the edge of Salt Lake City, Utah. In the 1960's a startling discovery was made quite by accident. A pair of scientists at Bell Laboratories detected background noise using a special low noise antenna. The strange thing about the noise was that it was coming from every direction and did not seem to vary in intensity much at all. If this static were from something on our world, like radio transmissions from a nearby airport control tower, it would only come from one direction, not everywhere. The scientists soon realized they had discovered the cosmic microwave background radiation. This radiation, which fills the entire Universe, is believed to be a clue to it's beginning, something known as the Big Bang. The image above is a Cosmic Background Explorer (COBE) image of the cosmic microwave background, the pink and blue colors showing the tiny fluctuations in it.

Credit:NASA,ESA Data compiled from The British Antarctic Study, NASA, Environment Canada, UNEP, EPA and other sources as stated and credited Researched by Charles Welch-Updated daily This Website is a project of the The Ozooe Hole Inc. Heinrich Hertz - Biography, Facts and Pictures Heinrich Hertz Lived 1857 – 1894. In a series of brilliant experiments Heinrich Hertz discovered radio waves and established that James Clerk Maxwell’s theory of electromagnetism is correct. Hertz also discovered the photoelectric effect, providing one of the first clues to the existence of the quantum world. The unit of frequency, the hertz, is named in his honor. Advertisements Beginnings Heinrich Rudolf Hertz was born on February 22, 1857 in the German port city of Hamburg. He was the firstborn of five children. His mother was Anna Elisabeth Pfefferkorn, the daughter of a physician. His father was Gustav Ferdinand Hertz, an attorney who became a Senator. His paternal grandfather, a wealthy Jewish businessman, had married into a Lutheran family and converted to Christianity.

Both of Heinrich’s parents were Lutherans, and he was raised in this faith. His parents, however, were more interested in his education than his religious advancement. School Aged six, Heinrich began at the Dr. Wichard Lange School in Hamburg. This was a private school for boys run by the famous educator Friedrich Wichard Lange. The school operated without religious influence; it used child-centered teaching methods, taking account of students’ individual differences. It was also strict; the students were expected to work hard and compete with one another to be top of the class. Heinrich enjoyed his time at school, and indeed was top of his class. Unusually, Dr. Lange’s school did not teach Greek and Latin – the classics – needed for university entry. The very young Heinrich had told his parents he wanted to become an engineer. When they looked for a school for him, they decided that Dr. Lange’s alternative focus, which included the sciences, was the best option. Heinrich Hertz, aged about 12, with his father, mother, and two younger brothers. Heinrich’s mother was especially passionate about his education.

Realizing he had a natural talent for making things and for drawing, she arranged draftsmanship lessons for him on Sundays at a technical college. He started these aged 11. Homeschool and Building Scientific Apparatus Aged 15, Heinrich left Dr. Lange’s school to be educated at home. He had decided that perhaps he would like to go to university after all. Now he received tutoring in Greek and Latin to prepare him for the exams. He excelled at languages, a gift he seems to have inherited from his father. Professor Redslob, a language specialist who gave Heinrich some tuition in Arabic, advised his father that Heinrich should become a student of oriental languages. Never before had he met anyone with greater natural talent. Heinrich also began studying the sciences and mathematics at home, again with the help of a private tutor. He had a colossal appetite for hard work. His mother said: When he sat with his books nothing could disturb him or draw him away from them. Although he had left his normal school, he continued attending the technical college on Sunday mornings. In the evenings he worked with his hands. He learned to operate a lathe.

He built models, and then began constructing increasingly sophisticated scientific apparatus, such as a spectroscope. He used this apparatus to do his own physics and chemistry experiments. Architecture and the Army Aged 17, Heinrich returned to school, the Johanneum, for a year in order to fully prepare for the classics exams that would admit him to university. Having passed the exams, he promptly changed his mind again, deciding to become an architect’s apprentice. He moved to Frankfurt, where by day he worked in an architect’s office, and in the evening he read physics books in German, and Ancient Greek literature in the original Ancient Greek – naturally! Architecture quickly bored him. In spring 1876, aged 19, he moved again, to Dresden, to study engineering. After only a few months he was drafted into the army for a year’s compulsory service. Although he enjoyed the discipline of army life, he found the army boring. Rather miserably, he wrote home at one point: “… day by day I grow more aware of how useless I remain in this world.” Heinrich Hertz Meanwhile, his interest in mathematics and physics continued to grow.

Becoming a Scientist Physics in Munich After completing his army service, the 20-year-old Hertz moved to Munich to begin an engineering course in October 1877. A month later, after much internal anguish, he dropped out of the course. He had decided that above all else he wanted to become a physicist. He enrolled at the University of Munich, choosing courses in advanced mathematics and mechanics, experimental physics, and experimental chemistry. After a successful year at Munich he moved to the University of Berlin because it had better physics laboratories than Munich. Berlin, Helmholtz, and Recognition In Berlin, aged 21, Hertz began working in the laboratories of the great physicist Hermann von Helmholtz. Helmholtz must have recognized a rare talent in Hertz, immediately asking him to work on a problem whose solution he was particularly interested in. The problem was the subject of a fierce debate between Helmholtz and another physicist by the name of Wilhelm Weber. The University of Berlin’s Philosophy Department, with Helmholtz’s encouragement, had offered a prize to anyone who could solve the problem: Does electricity move with inertia? Alternatively, we could frame the question in the form: Does electric current have mass?

Or, as framed by Hertz: Does electric current have kinetic energy? Hertz started work on the problem and quickly fell into a pleasant routine: attending a lecture each morning in either analytical dynamics or electricity & magnetism, carrying out experiments in the laboratory until 4pm, then reading, calculating, and thinking in the evening. He personally designed experiments which he thought would answer Helmholtz’s question. He began to really enjoy himself, writing home: “I cannot tell you how much more satisfaction it gives me to gain knowledge for myself and for others directly from nature, rather than to be merely learning from others and myself alone.” Heinrich Hertz The Prize In August 1879, aged 22, Hertz won the prize – a gold medal. In a series of highly sensitive experiments he had demonstrated that if electric current has any mass at all, it must be incredibly small. We have to bear in mind that when Hertz carried out this work the electron – the carrier of electric current – had not even been discovered. J. J. Thomson’s discovery was made in 1897, 18 years after Hertz’s work.

1.109 x 1030 electrons have a mass of 1 kg. The mass of 1.109 x 1030 humans would equal more than 30 solar systems like our own. The electron’s mass is tiny indeed. Other physicists began to notice just how dazzling Hertz’s work had been – the young student had put together experiments at the forefront of physics, personally modifying apparatus as needed. His practical skills, developed at home in the evenings, were proving to be priceless. His prize-winning work was published in the prestigious journal Annalen der Physik. Recognizing the incredible talent he had in his laboratory, Helmholtz now asked Hertz to compete for a prize offered by the Berlin Academy: verifying James Clerk Maxwell’s theory of electromagnetism. Maxwell had stated in 1864 that light was an electromagnetic wave and that other types of electromagnetic wave could exist. Doctor of Physics Hertz declined this project; he believed the attempt, with no guarantee of success, would take several years of work. He was ambitious and wanted to publish new results quickly to establish his reputation. Instead of working for the prize, he carried out a masterful three-month project on electromagnetic induction.

He wrote this up as a thesis. In February 1880, at the age of 23, his thesis brought him the award of a doctorate in physics. Helmholtz quickly appointed him as an assistant professor. Later that year Hertz wrote: “I grow increasingly aware, and in more ways than expected, that I am at the center of my own field; and whether it be folly or wisdom, it is a very pleasant feeling.” Heinrich Hertz 1880 Hertz stayed in Helmholtz’s laboratory until 1883, during which time he published 15 papers in academic journals. Mathematical Physics at Kiel Hertz was a gifted experimental physicist, but competition to secure a lectureship at Berlin was high. Instead, with Helmholtz’s support, Hertz became a lecturer in mathematical physics at the University of Kiel. This position, theoretical rather than experimental, extended his abilities. At Kiel he began to get to grips with Maxwell’s equations, writing in his diary: “Hard at Maxwellian electromagnetism in the evening.

Nothing but electromagnetism.” Heinrich Hertz Diary, May 1884 The result of Hertz’s work was a highly regarded paper comparing Maxwell’s electromagnetic theory with competing theories. He concluded that Maxwell’s theory looked the most promising. In fact he reworked Maxwell’s equations into a more convenient form. He later wrote: “From the start, Maxwell’s theory was the most elegant of all… the fundamental hypothesis of Maxwell’s theory contradicted the usual views, and was not supported by evidence from decisive experiments.” Heinrich Hertz 1890 This was because Hertz was one of the purest of pure scientists. He was interested only in designing experiments to entice Nature to reveal its mysteries to him. Once he had achieved this, he would move on, leaving any practical applications for others to exploit. The waves Hertz first generated in November 1886 quickly changed the world. By 1896 Guglielmo Marconi had applied for a patent for wireless communications. By 1901 he had transmitted a wireless signal across the Atlantic Ocean from Britain to Canada. Hertz’s discovery was the foundation stone for much of our modern communications technology.

Radio, television, satellite communications, and mobile phones all rely on it. Even microwave ovens use electromagnetic waves: the waves penetrate the food, heating it quickly from the inside. Our ability to detect radio waves has also transformed the science of astronomy. Radio astronomy has allowed us to ‘see’ features we can’t see in the visible part of the spectrum. And because lightning emits radio waves, we can even listen to lightning storms on Jupiter and Saturn. Scientists and non-scientists alike owe a lot to Heinrich Hertz. The Photoelectric Effect In 1887, as part of his work on electromagnetism, Hertz reported a phenomenon that had enormous implications for the future of physics and our fundamental understanding of the universe. It came to be known as the photoelectric effect. He shone ultraviolet light on electrically charged metal, observing that the UV light seemed to cause the metal to lose its charge faster than otherwise. He wrote the work up, published it in Annalen der Physik, and left it for others to pursue. It would have been a fascinating phenomenon for Hertz himself to investigate, but he was too wound up in his Maxwell project at the time. Experimenters rushed to investigate the new phenomenon Hertz had announced.

In 1899 J. J. Thomson, the electron’s discoverer, established that ultraviolet light actually ejected electrons from metal. This led Albert Einstein to rethink the theory of light. In 1905 he correctly proposed that light came in distinct packets of energy called photons. Photons of ultraviolet light have the right amount of energy to interact with electrons in metals, giving the electrons enough energy to escape from the metal. Einstein’s explanation of the photoelectric effect was one of the key drivers in constructing an entirely new way of describing atomic-scale events – quantum physics. Einstein was awarded the 1921 Nobel Prize in Physics for explaining the effect Hertz had discovered 34 years earlier. The photoelectric effect. Photons of UV light carry the correct amount of energy to eject electrons from a metal. Some Personal Details and the End In 1886, aged 29, Hertz married Elisabeth Doll in Karlsruhe. She was the daughter of a mathematician. They had two daughters, Johanna and Mathilde. Mathilde became an influential biologist, making thought-provoking discoveries in the field of how animals solve problems.

At the age of 35 Hertz became very ill, suffering severe migraines. Doctors thought he had an infection. They performed a series of operations, but Hertz continued to deteriorate. Heinrich Rudolf Hertz died aged 36 in Bonn on January 1, 1894 of blood-vessel inflammation resulting from immune system problems – specifically granulomatosis with polyangiitis. He was buried in his hometown of Hamburg, in the Ohlsdorf Cemetery. In 1930 the unit of frequency was named the hertz by the International Electrotechnical Commission. In 1960 the unit was made official by the General Conference on Weights and Measures. Advertisements Author of this page: The Doc Images digitally enhanced and colorized by this website. © All rights reserved. Cite this Page Please use the following MLA compliant citation: "Heinrich Hertz." Famous Scientists. famousscientists.org. 23 Nov. 2015. Web. < com2400 Scientists who discovered Electromagnetic Waves - Scientists who com2400 Scientists who discovered Electromagnetic Waves com2400 Scientists who discovered Electromagnetic Waves -...

SCHOOL View Full Document Scientists who discovered Electromagnetic Waves • James Clerk Maxwell- theorized that electric and magnetic fields travel through space, in the form of waves and at the constant speed of light. • Heinrich Hertz was the first to demonstrate the existence of electromagnetic radiation by building an apparatus to produce radio waves. Confusing names? • Electromagnetic energy or electromagnetic radiation • The travels through space in the form of waves • Electromagnetic waves • or "Radio Waves" Radio: radiation Guglielmo Marconi • Started developing a transmitter in high school, in his father's attic • An Italian inventor, developed the first practical radiotelegraph system. • He patented his wireless system in England in 1897 and found financing to establish the Marconi Wireless Telegraph Company. British Investment in Wireless • British Navy and commercial fleet were at the heart of their global power. • Hence the British were enthusiastic about wireless. • They already owned two thirds of the global submarine cables • Now this. Wireless Business • Marconi equipped ships at sea and made a fortune. He built a corporate empire that would span several continents and involve millions of dollars in investments.

• Marconi worked to monopolize the wireless business with his non- interconnection policy American Marconi Company and Trans-continental wireless • Marconi established the American subsidiary of the British Marconi Company in 1899. • Marconi demonstrated the power of his equipment in 1901 by conducting his first trans- Atlantic wireless transmission from Newfoundland, Canada to England. Wireless Communication • Advantages of Wireless compared to telegraph ◦ Communication between points without a wired connection. Eg. Ships at sea could communicate with other ships or with the shore. • Disadvantages: ◦ Huge antennas to detect signals ◦ Problem of weakening signals ◦ Morse code (compared to Telephone) Lee de Forest Audion tube • Father of radio • De Forest added a third element to Fleming valve and patented it as the Audion tube. • Audion tube made the wireless receivers more sensitive and improved radio This preview has intentionally blurred sections. Sign up to view the full version. This is the end of the preview. Sign up to access the rest of the document. TERM Principals of Television Joseph May's experiments with selenium.

Photoelectric cells com2400 Principals of Television Hertz Untersuchungen Ueber Die Ausbreitung Der Elektrischen Kraft (Investigations on the Propagation of Electrical Energy) Heinrich Hertz 1892 Heinrich Hertz was the first to send and receive radio waves. James Clerk Maxwell had mathematically predicted their existence in 1864. Between 1885 and 1889, as a professor of physics at Karlsruhe Polytechnic, he produced electromagnetic waves in the laboratory and measured their wavelength and velocity. He showed that the nature of their reflection and refraction was the same as those of light, confirming that light waves are electromagnetic radiation obeying the Maxwell equations. All of these findings were first published in the journal Annalen der Physik,(see below right) then in Hertz's first book, Untersuchungen Ueber Die Ausbreitung Der Elektrischen Kraft (Investigations on the Propagation of Electrical Energy), shown at right. His book is considered to be one of the most important works of science. This is where he first describes his confirmation of the existence of electromagnetic waves.

Annalen der Physik und Chemie is one of the oldest physics journals worldwide. The journal, still in publication today, publishes original papers in the areas of experimental, theoretical, applied and mathematical physics and related areas. Hertz's Experiment: There are 12 complete volumes of Annalen der Physik und Chemie in my collection. Included are Hertz's many papers proving the Maxwell hypothesis on the propagation of electromagnetic waves. These papers laid the foundation for the development of radio and electromagnetic wave transmission applications. Also included are more Hertz papers plus others by Roentgen, Planck, Boltzmann, Angstrom, Helmholtz. Heinrich Hertz | A HISTORY OF SCIENCE A HISTORY OF SCIENCE 1864 – Scotland The Scottish physicist examined Faraday’s ideas concerning the link between electricity and magnetism interpreted in terms of fields of force and saw that they were alternative expressions of the same phenomena. Maxwell took the experimental discoveries of Faraday in the field of electromagnetism and provided his unified mathematical explanation, which outlined the relationship between magnetic and electric fields. He then proved this by producing intersecting magnetic and electric waves from a straightforward oscillating electric current.

‘Four equations that express mathematically the way electric or magnetic fields behave’ In 1831 – following the demonstration by HANS CHRISTIAN OERSTED that passing an electric current through a wire produced a magnetic field around the wire, thereby causing a nearby compass needle to be deflected from north – MICHAEL FARADAY had shown that when a wire moves within the field of a magnet, it causes an electric current to flow along the wire. This is known as electromagnetic induction. In 1864 Maxwell published his ‘Dynamical Theory of the Electric Field’, which offered a unifying, mathematical explanation for electromagnetism. In 1873 he published ‘Treatise on Electricity and Magnetism’. The equations are complex, but in general terms they describe: a general relationship between electric field and electric charge a general relationship between magnetic field and magnetic poles how a changing magnetic field produces electric current how an electric current or a changing electric field produces a magnetic field The equations predict the existence of electromagnetic waves, which travel at the speed of light and consist of electric and magnetic fields vibrating in harmony in directions at right angles to each other. The equations also show that light is related to electricity and magnetism.

Maxwell worked out that the speed of these waves would be similar to the speed of light and concluded, as Faraday had hinted, that normal visible light was a form of electromagnetic radiation. He argued that infrared and ultraviolet light were also forms of electromagnetic radiation, and predicted the existence of other types of wave – outside the ranges known at that time – which would be similarly explainable. Verification came with the discovery of radio waves in 1888 by HEINRICH RUDOLPH HERTZ. Further confirmation of Maxwell’s theory followed with the discovery of X-rays in 1895. JAMES CLERK MAXWELL Maxwell undertook important work in thermodynamics. Building on the idea proposed by JAMES JOULE , that heat is a consequence of the movement of molecules in a gas, Maxwell suggested that the speed of these particles would vary greatly due to their collisions with other molecules. In 1855 as an undergraduate at Cambridge, Maxwell had shown that the rings of Saturn could not be either liquid or solid. Their stability meant that they were made up of many small particles interacting with one another. In 1859 Maxwell applied this statistical reasoning to the general analysis of molecules in a gas.

He produced a statistical model based on the probable distribution of molecules at any given moment, now known as the Maxwell-Boltzmann kinetic theory of gases. He asked what sort of motion you would expect the molecules to have as they moved around inside their container, colliding with one another and the walls. A reasonably sized vessel, under normal pressure and temperature, contains billions and billions of molecules. Maxwell said the speed of any single molecule is always changing because it is colliding all the time with other molecules. Thus the meaningful quantities are molecular average speed and the distribution about the average. Considering a vessel containing several different types of gas, Maxwell realized there is a sharp peak in the plot of the number of molecules versus their speeds. That is, most of the molecules have speeds within a small range of some particular value. The average value of the speed varies from one kind of molecule to another, but the average value of the kinetic energy, one half the molecular mass times the square of the speed, (1/2 mv2), is almost exactly the same for all molecules. Temperature is also the same for all gases in a vessel in thermal equilibrium.

Assuming that temperature is a measure of the average kinetic energy of the molecules, then absolute zero is absolute rest for all molecules. The Joule-Thomson effect, in which a gas under high pressure cools its surroundings by escaping through a nozzle into a lower pressure environment, is caused by the expanding gas doing work and losing energy, thereby lowering its temperature and drawing heat from its immediate neighbourhood. By contrast, during expansion into an adjacent vacuüm, no energy is lost and temperature is unchanged. The explanation that heat in gas is the movement of molecules dispensed with the idea of the CALORIC fluid theory of heat. The first law of thermodynamics states that the heat in a container is the sum of all the molecular kinetic energies. Thermal energy is another way of describing motion energy, a summing of the very small mechanical kinetic energies of a very large number of molecules; energy neither appears nor disappears. According to BOYLE ’s, CHARLES ’s and GAY-LUSSAC ’s laws, molecules beating against the container walls cause pressure; the higher the temperature, the faster they move and the greater the pressure. This also explains Gay-Lussac’s experiment.

Removing the divider separating half a container full of gas from the other, evacuated half allows the molecules to spread over the whole container, but their average speed does not change. The temperature remains the same because temperature is the average molecular kinetic energy, not the concentration of caloric fluid. In 1871 Maxwell became the first Professor of Physics at the Cavendish Laboratory . He died at age 48. MICHAEL FARADAY (1791-1869) 1831 – England ‘A changing magnetic field around a conductor produces an electric current in the conductor. The size of the voltage is proportional to the rate of change of the magnetic field’ This phenomenon is called ‘electromagnetic induction’ and the current produced ‘induced current’. Induction is the basis of the electric generator and motor. MICHAEL FARADAY Faraday developed HANS CHRISTIAN OERSTED ’s 1820 discovery that electric current could deflect a compass needle. In his experiment Faraday wrapped two coils of insulated wire around opposite sides of an iron ring. One coil was connected to a battery, the other to a wire under which lay a magnetic compass needle.

He anticipated that if he passed a current through the first wire it would establish a field in the ring that would induce a current in the second wire. He observed no effect when the current was steady but when he turned the current on and off he noticed the needle moving. He surmised that whenever the current in the first coil changed, current was induced in the second. To test this concept he slipped a magnet in and out of a coil of wire. While the magnet was moving the compass needle registered a current, as he pushed it in it moved one way, as he pulled it out the needle moved in the opposite direction. This was the first production of electricity by non-chemical means. In 1831, by rotating a copper disc between the poles of a magnet, Faraday was able to produce a steady electric current. This was the world’s first dynamo. NEWTON , with his concept of gravity, had introduced the idea of an invisible force that exerted its effect through empty space, but the idea of ‘action-at-a-distance’ was rejected by an increasing number of scientists in the early nineteenth century.

By 1830, THOMAS YOUNG and AUGUSTIN FRESNEL had shown that light did not travel as particles, as Newton had said, but as waves or vibrations. But if this was so, what was vibrating? To answer this, scientists came up with the idea of a weightless matter, or ‘aether’. Faraday had rejected the concept of electricity as a ‘fluid’ and instead visualised its ‘fields’ with lines of force at their edges – the lines of force demonstrated by the pattern of iron fillings around a magnet. This meant that action at a distance simply did not happen, but things moved only when they encountered these lines of force. He believed that magnetism was also induced by fields of force and that it could interrelate with electricity because the respective fields cut across each other. Proving this to be true by producing an electric current via magnetism, Faraday had demonstrated electromagnetic induction. When Faraday was discovering electromagnetic induction he did so in the guise of a natural philosopher. Physics, as a branch of science, was yet to be given a name.

The Russian physicist HEINRICH LENZ (1804- 65) extended Faraday’s work when in 1833 he suggested that ‘the changing magnetic field surrounding a conductor gives rise to an electric current whose own magnetic field tends to oppose it.’ This is now known as Lenz’s law. This law is in fact LE CHATELIER ‘s principle when applied to the interactions of currents and magnetic fields. Fluctuating Electromagnetic Fields and EM Waves It took a Scottish mathematician by the name of JAMES CLERK MAXWELL to provide a mathematical interpretation of Faraday’s work on electromagnetism. Describing the complex interplay of electric and magnetic fields, he was able to conclude mathematically that electromagnetic waves move at the speed of light and that light is just one form of electromagnetic wave. This led to the understanding of light and radiant heat as moving variations in electromagnetic fields. These moving fields have become known collectively as radiation. Faraday continued to investigate the idea that the natural forces of electricity, magnetism, light and even gravity are somehow ‘united’, and to develop the idea of fields of force. He focused on how light and gravity relate to electromagnetism.

After experimenting with many transparent substances, he tried a piece of heavy lead glass which led to the discovery of the ‘Faraday Effect’ in 1845 and proved that polarised light may be affected by a magnet. This opened the way for enquiries into the complete spectrum of electromagnetic radiation. In 1888 the German physicist HEINRICH HERTZ confirmed the existence of electromagnetic waves – in this case radio waves – traveling at the speed of light. The unit of capacitance, farad (F) is named in honour of Faraday. HEINRICH RUDOLPH HERTZ (1857- 94) 1888 – Germany ‘Radio waves can be produced by electric sparks. They have the same speed as light and behave as light’ Hertz’s discovery provided the basis of radio broadcasting. In 1864 MAXWELL ‘s equations predicted the existence of electromagnetic waves. His thinking had shown that electromagnetic waves could be refracted, reflected and polarized in the same way as light. Hertz was able to measure the speed of these waves and to show that the speed is the same as that of light.

Hertz hypothesised that he could experimentally examine the waves by creating apparatus to detect electromagnetic radiation. He devised an electric circuit with a gap that would cause a spark to leap across when the circuit was closed. If Maxwell’s theory was correct and electromagnetic waves were spreading from these oscillator sparks, appropriately sensitive equipment should pick up the waves generated by the spark. Hence he constructed the equivalent of an antenna. His simple receiver consisted of two small balls at the ends of a loop of wire, separated by a small gap. This receiver was placed several yards from the oscillator and the electromagnetic waves would induce a current in the loop that would send sparks across the small gap. This was the first transmission and reception of electromagnetic waves. He called the waves detected by the antenna ‘Hertzian waves’. We are now familiar with all the types of electromagnetic waves that make up the complete electromagnetic spectrum. They all travel with the speed of light and differ from each other in their frequency. We measure this frequency in hertz.

It was left to the Italian electrical engineer GUGLIELMO MARCONI to refine this equipment into a device that had the potential of transmitting a message and to develop technology for the practical use of Hertzian waves – when they became commonly known as radio waves. Further experimentation showed that these waves had the properties that Maxwell had predicted. As well as being important as a newly discovered phenomenon, Hertz’s discovery helped to prove that Maxwell had been correct when he suggested that light and heat were forms of electromagnetic radiation. Radio waves are electromagnetic waves. Other main kinds of electromagnetic waves are: gamma rays; X-rays; ultra-violet radiation; visible light; infrared radiation and microwaves. This radiation was behaving in all the ways that would be expected for waves, the nature of the vibration and the susceptibility to reflection and refraction were the same as those of light and heat waves. Hertz found that they could be focused by concave reflectors. Experimenting further, Hertz spotted that electrical conductors reflect this electromagnetic radiation and that non-conductors allow most of the waves to pass through. In honour of Hertz’s achievements, the SI unit of frequency, the hertz (Hz), was named after him.

Hertz’s discoveries came at an early age. The German physicist died at the age of thirty-six. Electronics/History/Chapter 2 - Wikibooks, open books for an open world Electronics/History/Chapter 2 A Wikibookian suggests that this book or chapter be merged into History of Electronics . Please discuss whether or not this merge should happen on the discussion page . Electricity and Magnetism: 1600-1875 [1] Contents Luigi Galvani[ edit ] Luigi Galvani (September 9, 1737 - December 4, 1798) was an Italian physician and physicist who lived and died in Bologna. Dissecting a frog at a table where he had been conducting experiments with static electricity, Galvani touched an exposed sciatic nerve of the frog with his metal scalpel, which had picked up a charge. At that moment, he saw the dead frog's leg kick as if in life. The observation made Galvani the first investigator to appreciate the relationship between electricity and animation--or life. He is typically credited with the discovery of biological electricity.

Galvani coined the term animal electricity to describe whatever it was that activated the muscles of his specimens. Along with contemporaries, he regarded their activation as being generated by an electrical fluid that is carried to the muscles by the nerves. The phenomenon was dubbed "galvanism," after Galvani, on the suggestion of his peer and sometime intellectual adversary Alessandro Volta. Galvani's investigations led shortly to the invention of an early battery, but not by Galvani, who did not perceive electricity as separable from biology. Galvani saw electricity instead as the essence or the stuff itself of life, which he regarded vitalistically. Thus it was Volta who built the first battery, which became known therefore as a voltaic pile. While, as Galvani believed, all life is indeed electrical--in that all living things are made of cells and every cell has a cell potential--biological electricity has the same chemical underpinnings as the flow of current between electrochemical cells, and thus can be recapitulated in a way outside the body. Volta's intuition was correct as well. Galvani's name also survives in the Galvanic cell, the galvanometer and "galvanize".

Alessandro Volta[ edit ] Alessandro Giuseppe Antonio Anastasio Volta (February 18, 1745 - March 5, 1827) was an Italian physicist known especially for the development of the electric battery. Late in life, he received the title of Count. De vi attractiva ... Volta was born and educated in Como, Italy, where he became professor of physics at the Royal School in 1774. His passion had always been the study of electricity, and still a young student he had even written a poem in Latin on this fascinating new discovery.De vi attractiva ignis electrici ac phaenomenis inde pendentibus is his first scientific paper. In 1775 he devised the electrophorus, a device that produced a static electric charge. In 1776-77 he studied the chemistry of gases, discovered methane, and devised experiments such as the ignition of gases by an electric spark in a closed vessel. In 1779 he became professor of physics at the University of Pavia, a chair he occupied for 25 years.

In 1794 Volta married Teresa Peregrini, daughter of Count Ludovico Peregrini; the couple had three sons. In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, he developed the so-called voltaic pile, a forerunner of the electric battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver. Initially he experimented with individual cells in series, each cell being a wine goblet filled with brine into which the two dissimilar electrodes were dipped. The electric pile replaced the goblets with cardboard soaked in brine. (The number of cells, and thus the voltage it could produce, was limited by the pressure, exerted by the upper cells, that would squeeze all of the brine out of the cardboard of the bottom cell.) Templo Voltiano In honor of his work in the field of electricity, Napoleon made him a count in 1810; in 1815 the Emperor of Austria named him a professor of philosophy at Padua.

Volta is buried in the city of Como in Italy; the Templo Voltiano near Lake Como is a museum devoted to explaining his work; his original instruments and papers are on display there. The building appeared, along with his portrait, on Italian currency before the introduction of the Euro. An electrophorus is a simple plate capacitor used to collect static charge produced as a result of friction, devised in 18th century by Johannes Wilcke and Alessandro Volta. The electrophorus consists of a dielectric plate on a metal surface and a metal plate with an insulating handle. First, the dielectric plate is triboelectrically charged, that is, by friction. Then, the metal plate is placed onto the dielectric plate. The metal plate charges by induction - the side facing the charged dielectric plate charges opposite to the charge of plate, while the side facing away from the dielectric charge attains the same sign of charge as the dielectric plate, thus making the metal plate electrically neutral as a whole. Then, the side facing away from the dielectric plate is momentarily grounded. Finally, the metal plate, now consisting only one sign of charge, is lifted.

The Voltaic Pile was invented by Alessandro Volta in 1800. He demonstrated that when certain metals and chemicals come into contact with each other they can produce an electrical current. He placed together several pairs of copper and zinc discs separated by paper soaked in salt water, and an electrical current was produced. This was the first chemical battery. For his contributions to the study of electricity, the SI unit called the volt was named after Volta. In 1881 an important electrical unit was named the volt was named in his honor. Heinrich Hertz[ edit ] Heinrich Rudolf Hertz (February 22, 1857 - January 1, 1894), was the German physicist for whom the hertz, the SI unit of frequency, is named. In 1888, he was the first to demonstrate the existence of electromagnetic radiation by building apparatus to produce radio waves. Hertz was born in Hamburg, Germany, to a Jewish family that had converted to Christianity. His father was an advocate in Hamburg, his mother the daughter of a doctor. While at school, he showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit.

He studied sciences and engineering in the German cities of Dresden, Munich and Berlin. He was a student of Gustav R. Kirchhoff and Hermann von Helmholtz. He obtained his PhD in 1880, and remained a pupil of Helmholtz until 1883 when he took a post as a lecturer in theoretical physics at the University of Kiel. In 1885 he became a full professor at the University of Karlsruhe where he discovered electromagnetic waves. Following Michelson's 1881 experiment (precursor to the 1887 Michelson-Morley experiment) which disproved the existence of Luminiferous aether he reformulated Maxwell's equations, to take the new discovery into account. Through experimentation, he proved that electric signals can travel through open air, as had been predicted by James Clerk Maxwell and Michael Faraday, and which is the basis for the invention of radio. He also discovered the photoelectric effect (which was later explained by Albert Einstein) when he noticed that a charged object loses its charge more readily when illuminated by ultraviolet light. He died in Bonn, Germany.

His nephew Gustav Ludwig Hertz was a Nobel Prize winner, and Gustav's son Carl Hellmuth Hertz invented medical ultrasonography. See also People * Wilhelm Röntgen * Hans Christian Ørsted * Guglielmo Marconi * Gustav Ludwig Hertz * Hermann von Helmholtz * James Clerk Maxwell * Nikola Tesla * Wilhelm Röntgen Lists and histories * Electromagnetism timeline * Timeline of mechanics and physics * List of physicists * Radio history * Wireless telegraphy * List of people on stamps of Germany * List of physics topics Electromagnetic radiation * Frequency o Hertz * Microwave * X-ray * Photoelectric effect * Radar * Luminiferous aether Other EM waves[ edit ] The existence of electromagnetic waves, i.e. microwaves, was predicted by James Clerk Maxwell in 1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building apparatus to produce radio waves.

spectrum[ edit ] It was Sir Isaac Newton in 1666 who first used the word spectrum to refer to the celebrated Phenomenon of Colours which can be extracted from sunlight, by a glass prism. Infared[ edit ] History In 1800 the English astronomer William Herschel held a mercury thermometer in the spectrum produced by a glass prism to measure the heat content of different coloured lights. He found that the thermometer registered an increase in temperature even when held beyond the red end of the spectrum, where there was no visible light. This was the first experiment to show that heat could be transmitted by an invisible form of light.

Question: Which scientist was the first, in 1888, to demonstrate the existence of electromagnetic waves?
Answer: (Heinrich Rudolf) HERTZ